Pulse detonation engines (PDE) represent an energy conversion device that has existed for some time, but which have recently received increased attention. Such engines generally combust fuel and an oxidant in a chamber, or combustor, to provide a component of thrust or force in an intended direction. The combustion occurs in the manner of discrete, i. e. pulsed, detonations. The present invention is concerned with configurations that employ an open-ended chamber, such as a rocket nozzle, that may be employed for a component of thrust. A principal application for such engines is as a thrust source to propel an aerospace vehicle in the atmosphere or the vacuum of space. In such instance, the PDE is also a rocket engine.
The development of PDE's requires the ability to quickly fill an open-ended chamber with a detonatable mixture while purging the exiting exhaust gases with minimal mixing. For pulse detonation rocket engine applications where the open end of the chamber is likely to be exposed to a vacuum, the fresh charge of detonatable mixture must be contained in the chamber for several milliseconds before the detonation is initiated. Further, the mixture must be pressurized to levels on the order of 50-1000 psi with the chamber open to vacuum in order to generate thrust competitive with conventional rocket engines. Moreover, the process must be done at rates approaching or exceeding 100 Hz.
Two alternative concepts that may be used to control chamber pressure are mechanical valves and fixed throats, but each has significant limitations. The complexity and weight of a mechanical valve, combined with durability and sealing requirements in the hot exhaust flow, suggest that it would be difficult and/or impractical to implement in this application and environment. A fixed throat near the chamber exit would restrict the flow, allowing the chamber to be pressurized with high propellant flow rates while some propellant is lost through the exit. This arrangement suffers from the loss of efficiency due to propellant leakage during the fill process and from thrust reduction due to the reduced exit area of the throat.
A further discussion of the physics and operation of PDE's is contained in several U.S. Patents by T. R. Bussing, including U.S. Pat. Nos. 5,513,489; 5,353,588; and 5,345,758. These patents discuss the use of a rotary valve, but only to control the admission of propellant and oxidant to each of multiple combustor chambers rather than to also control the pressure developed in the chamber. They rely upon an approach that uses multiple chambers each feeding into a common, restricted throat.
Accordingly, it is an object of the invention to provide an arrangement that is durable, relatively efficient, and simple, for controlling the pressure of fluids, such as propellants, in the chamber of a pulse detonation engine.
It is a further object to provide a pulse detonation engine in which the timing of detonation is optimized or tuned in accordance with the present invention.
It is a still further object to provide improved fluid injection mechanism for use with the pulse detonation engine in accordance with the invention.